Sebastian is the head scientist for Team Rocket. It is said that he is one of the most famous Team Rocket scientists of all time. Attila, Hun, and Tyson of Team Rocket apparently take orders from him. Given that Sebastian is always seen with Rocket members wearing the grey uniforms, it can be assumed that they are part of a special squad whose specific purpose is to work for Sebastian and the research department, probably accompanying him to test and protect his experiments out in the field and further the important research being done for Team Rocket. Tyson seems to have a great respect and reverence for Professor Sebastian. Attila and Hun seem to have a more casual relationship with him. In the English dub it is implied that Sebastian and Hun have known each other for quite some time though he has never met Attila before. In the original version, neither had met him before the events of that episode. It is not known why this change was made.

He appeared in The Legend of Thunder!, and later appeared in Talkin' 'Bout an Evolution and Rage of Innocence. He seems to be a very calm, cool, and collected individual. He is a researcher and appears to have a rather large group of scientists and team rocket members under his command. In Legend of Thunder! he is seen briefing Attilla and Hun, and giving orders to a group of about 10-15 scientists. In the Red Gyarados episodes, he is seen in charge of an even bigger group of scientists. He also gives orders to Tyson, who gives orders to the numerous Team Rocket grunts on site, including Jessie, James, and Meowth (he is actually identified as the "squadron leader" in the English dub). Professor Sebastian created The Crystal System that could trap Electric-type Pokémon and the Legendary PokémonRaikou, and he also created a beam that could make Pokémon evolve, called the Evolution Inducement Ray, which he so lovingly referred to in Talkin' Bout an Evolution as "my beautiful new invention".

He later made a small cameo appearance in the ninth movie. He is seen with Attila and Hun, and they have apparently succeeded in the capture of Rayquaza. We see it hooked up to some kind of large device, and Sebastian is doing some kind of experiment on it involving electricity. It is unknown what exactly he was doing to it, what became of the experiment or if Rayquaza ever got away. This happened in the opening for Pokémon Ranger and the Temple of the Sea.

Professor Sebastian is considerably shorter than most other adults seen in the Pokémon anime. Some of his notable physical characteristics include a triangular goatee and a stark white streak in his bangs, which stands out against the rest of his hair. His hair color was depicted as jet black in the Gyarados episodes, and a lighter more obvious grey in The Legend of Thunder. Some fans believe that the white streak in his hair is an indication of his age, which is estimated to be somewhere in the 40-60 range, but some believe it is actually a Mallen Streak, meaning it is hereditary and he has had it from birth. Sebastian has heavily lidded eyes, with very small black pupils, giving him an always smug or even tired appearance. He is almost always smiling in a way that seems more indicative of his self-important attitude rather than an expression of genuine happiness.

Most scientists in the Pokémon anime are seen wearing an open white labcoat over a dress shirt and tie, often worn with khaki pants or slacks and dress shoes, Sebastian dresses differently. He wears a closed off-white jacket with a high collar, a pocket on the left breast of the jacket, and a dark blue accent starting on either side of the collar and tapering in a triangle to form a single line going down the front. He wears solid white dress pants and black dress shoes. It is unknown if this unique outfit is an indication of his rank within Team Rocket or if it is simply a reflection of his personal style.

Though he is seen in temporary possession of many rare and powerful pokémon such as the Red Gyarados, Raikou, and Rayquaza, Sebastian is never seen with any pokémon of his own. That is to say, he has never called any pokémon into or out of a pokéball before that we have seen, and he has never been seen involved in a pokémon battle. Since he has Tyson, Attila, and Hun present to take care of his light work with their rather powerful arsenal of pokémon, it is unknown if Professor Sebastian even has a pokémon. It is logical to assume he does, since almost everyone in the pokémon world keeps at least one even if it's nothing more than a pet. Some fan speculation about what kind of pokémon he might have include Porygon, Porygon2, Porygon-Z, Magneton, Mightyena, Persian, and Serperior, among others. Some have suggested that he would probably have some kind of electric pokémon, since electricity seems to be a constant theme in his scientific works we have seen so far.